Linear polyethylene resins including high density polyethylene (HDDP) and linear low density ethylene copolymers (LLDPE) are difficult to process through conventional extrusion equipment designed for branched polyethylene prepared by high pressure polymerization. Linear polyethylenes are extruded at lower output rates because of high head pressure and power consumption. This is necessary because of their melt rheological characteristics, particularly high shear viscosity. In addition, linear polyethylene films and bags often exhibit poor appearance due to melt fracture. It has been concluded that the melt fracture mechanism for linear polyethylenes is different from the branched species. Furthermore, the use of linear polyethylenes in clear film packaging is limited because of its poor optical properties. The optical properties of linear polyethylene films is related to the rheological behavior of the melt and the morphological nature of the resin.
In many applications blends of linear polyethylenes with polyamides are desirable to obtain improved physical properties and barrier properties. But blends of linear polyolefins and polyamides are also diffcult to extrude and the the extrudates exhibit the same or similar defects as observed when linear polyethylenes are extruded alone. My U.S. Pat. No. 4,607,072 which is incorporated herein by reference discloses the use of fatty acid amides as additives to linear polyolefins for the purpose of improving processability of linear polyolefins particularly in the extrusion of films.
In accordance with this invention fatty acid derivatives such as fatty acid amides are added to blends of linear polyethlenes and polyamides to achieve better processing characteristics.